This invention relates to a speed change control system for automatic transmissions used in combination with a DC electric motor in electric automobiles. More particularly it relates to an automatic transmission control system of the type recited specifically designed for minimizing the shock or impact caused by the reaction to the locking of elements of the change gear unit during the operation of the frictional coupling means to effect speed change or when transmitting motive power to the rotational elements.
In automatic transmissions of electric automobiles there is a difficult problem that excess shock is produced by the action of the frictional coupling means during speed change. Several methods have been proposed to alleviate such shock of transmission, such as for example by controlling hydraulic pressure supplied to the servo mechanism of the frictional coupling device to smooth its operation. Such means, however, gave rise to a new problem of deterioration by wear of the frictional coupling device as it slides. Thus, none of the heretofore proposed methods has proved to be a perfect solution to the problem.
In view of the above, the present invention has the object of effectively lessening the transmission shock. The present invention takes into account the fact that the transmission output shaft torque fluctuates widely at the time of speed change thereby causing shock of transmission. Consequently the control system of the present invention prevents such fluctuation of the transmission output shaft torque by using the output torque of a DC electric motor to counteract the fluctuations thereby allowing extremely smooth transmission of power.